Abstract

In recent years, an increasing body of evidence has emerged postulating that right
ventricular (RV) - pulmonary artery (PA) ventriculoarterial coupling may offer insight
into the transition from RV adaptation to RV maladaptation in different cardiopulmonary
disorders and heart failure. RV-PA ventriculoarterial coupling is a matching between
RV contractility (Ees – End-Systolic Elastance) and afterload (Ea – Effective Arterial
Elastance). While ventriculoarterial coupling has been extensively described in the LV
and used to determine optimal conditions for the efficient transfer to blood from the
ventricle into the aorta, it remains unclear whether this relationship can be translated to
the thinner walled RV that pumps at lower pressures against a more compliant
pulmonary vascular system. Therefore, the pressure-volume (PV)-loop studies in this
thesis were undertaken to assess whether ventriculoarterial uncoupling due to
pressure overload or sub-optimal contractility contributed to further RV diastolic
dysfunction.
An in-vivo porcine model of RV-PA ventriculoarterial coupling was developed to define
optimal conditions. This animal model was used to provide insights into two clinical
patient groups that have RV dysfunction due to: i) long-term RV pressure overload in
patients with a clinical diagnosis of chronic thromboembolic disease (CTED) /
pulmonary hypertension (CTEPH); and ii) aortic valve stenosis transmitted by
ventricular interdependence and septal wall reconfiguration in patients treated with
transcatheter aortic valve implantation (TAVI).
The animal model determined an ventriculoarterial coupling ratio at maximal stroke
work (Ees/Eamax sw = 0.68±0.23) threshold, below which cardiac output and RV stroke
work fell. In the first clinical study this threshold was used to reclassify 25% of a cohort
of patients with CTED or CTEPH. Two patients with CTED were identified with an
EesEa below 0.68 suggesting occult RV dysfunction whilst three patients with CTEPH
demonstrated Ees/Ea≥0.68 suggesting residual RV energetic reserve. In the second
clinical study ventricular interdependence phenomena caused septal reconfiguration
and increased RV volumes after valve deployment, due to the reduction in LV
afterload. However, the rapid pacing (RP) protocol used to stabilise the aortic valve
during deployment also caused RP-induced ischemia and stunning. This resulted in the
reduction of Ees and led to Ees/Ea uncoupling and further diastolic dysfunction.
This work has demonstrated that: Low Ees/Ea aligns with features of RV maladaptation
in CTED. Characterization of Ees/Ea in CTED may allow for better identification of
occult RV dysfunction in patients with otherwise normal pulmonary hemodynamics; and
a reduction in Ees following TAVI correlates with increased RV diastolic dysfunction,
due to RP-induced ischemia and stunning.